Overview of three algae removal methods: The following paragraph is taken from a graduation thesis:

"The aging of chemicals is relatively fast, which can quickly kill algae. Therefore, unless emergency and health and safety permit, chemical algae killing is generally not appropriate. At present, chemical algaecides widely used include organic bromine, copper sulfate, copper chloride, potassium permanganate, etc., among which copper sulfate is the most commonly used. The harm of copper ions to cyanobacteria and other algae has been reported a lot (and Li Ping, 200 1). Chemical algae removal can be effective in a short time, but the secondary pollution caused by dead algae and the biological enrichment and biomagnification of chemicals have a great negative impact on the whole ecosystem. Long-term use of low-concentration chemicals will make algae resistant, and the toxic effect on algae is copper ion, which inhibits photosynthesis, cell division and nitrogen fixation. Cu2+ will cause secondary pollution to zooplankton and fish, so it can only be used as an emergency measure and cannot be used for the second time in the same water area within 3 years.

Physical method is the most direct, which can directly remove algae from water without causing secondary pollution, but it often requires a lot of manpower and energy, so it can only be confined to local waters of small water bodies or large water bodies. In addition to measures such as river closure, dredging, dilution and sewage diversion, physical methods have also developed algae removal methods such as mechanical or manual salvage, ultrasonic wave and clay adsorption, shading technology, etc. For example, (Shen et al. 2004) used mechanical algae removal method to remove algae in Dianchi Lake, Yunnan Province. Zou Hua et al. (2007) think that chitosan modified clay has good algae removal effect under the condition of low ionic strength, and it is an emergency algae removal technology suitable for fresh water (low salt content) such as lakes, reservoirs and rivers.

Biological control of algae from the ecological point of view, through the nutritional competition between organisms and the relationship between grazing and feeding to control cyanobacteria bloom. This method does not cause secondary pollution and has the advantages of economy, high efficiency and rationality (Wang &; Lu Kaihong, 2004). At present, the main research and attempts are microbial control, algae-eating organisms, aquatic plant inhibition and other methods. "